The assembly of an automobile engine requires the installation of pistons into the engine's cylinder sleeves. Prior to this installation, however, each piston must be fitted with a connecting rod. The connecting rod is connected to the piston through the use of a steel pin, known as a wrist pin. The wrist pin is press fit into mounting holes provided by the piston, and the connecting rod moves freely on the wrist pin. For the wrist pin to be pressed into the piston, it is necessary to heat the piston to a predetermined temperature causing adequate expansion of the mounting holes to allow the wrist pin to fit. The heated pistons are then installed into the engine's cylinder sleeves. In their heated state, the pistons are expanded and therefore will fit more tightly into the cylinder sleeves than when the pistons are cool.
Many engines have steel cylinder sleeves and aluminum pistons. During normal engine operation, the aluminum pistons expand more than the associated steel cylinder sleeve. To allow for the excess expansion by the piston, a predetermined cold temperature clearance between the piston and the engine cylinder sleeve is provided during production to prevent the piston from fitting too tightly for proper operation when the engine becomes hot during normal operation.
A problem arises with engines using a silica impregnated aluminum cylinder sleeve and an aluminum piston. Since both the sleeve and the piston are made of essentially the same material, they both expand essentially the same amount due to the heating from engine operation, eliminating the need for the cold temperature clearance. However, since the normal tolerances or spaces between the piston's outside diameter and the cylinder sleeve's inside diameter are now very close, the parts will no longer fit together when the piston alone is heated to install the wrist pin.
Therefore, there exists a need in the art for a method of installing a piston into a cylinder sleeve, wherein the piston is initially at an elevated temperature relative to the cylinder sleeve and wherein the initial inner diameter of the cylinder sleeve is less than or equal to the outer diameter of the piston.